Field of the Invention
The present invention relates to an image pickup apparatus, an image pickup system, and a method of driving an image pickup apparatus.
Description of the Related Art
There has been proposed an image pickup apparatus of a pupil division system capable of performing both focus detection and image pickup. For example, in an image pickup apparatus disclosed in Japanese Patent Application Laid-Open No. 2013-106194, one pixel includes a photoelectric conversion element A and a photoelectric conversion element B, and a microlens is formed on an upper side of the photoelectric conversion element A and the photoelectric conversion element B. Further, a pupil of a photographing lens and the photoelectric conversion elements are arranged so as to have a substantially conjugate positional relationship. With such a configuration, while focus detection is performed based on signals of the photoelectric conversion element A and the photoelectric conversion element B, the signals of the photoelectric conversion element A and the photoelectric conversion element B are added, to thereby obtain a signal for forming an image. Further, in Japanese Patent Application Laid-Open No. 2013-106194, after the signal is read from the photoelectric conversion element A, the signal of the photoelectric conversion element B is added to the signal of the photoelectric conversion element A, to thereby read a signal for forming an image.
In the image pickup apparatus disclosed in the above-mentioned literature, an attempt has not been made to improve the transfer efficiency of a charge from a photoelectric conversion element to an amplification unit.